Hi Nomadist welcome to the forums. \
One problem you're going to find is that any added wheels or rollers will further decrease your ground clearance.
Have you tried entering driveways at a 30 - 45 degree angle instead if straight on? This may buy you some clearance as one wheel can start lifting the coach before the hitch in the center hits.
Look under at the mounting point of the springs to the rear axle. If you have leaf springs and if they sit on top of the axle you can easily add a spacer to gain some height.
Air bags in the rear will help as well/ But make sure they are ones that you can adjust from the drivers seat.